Method for the production of composite elements based on isocyanate-based foams

ABSTRACT

An apparatus for application of liquids to a continuously conveyed outer layer having a rotating plate which is horizontal and parallel to the outer layer or with a deviation of up to 15° from horizontal, wherein a liquid applied to the rotating plate is ejected centrifugally from the rotating plate via rotation and then, via gravity, passed onto the outer layer below the rotating plate, is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of prior U.S. patentapplication Ser. No. 11/574,146, filed on Feb. 23, 2007, the disclosureof which is incorporated herein by reference in its entirety. The parentapplication is the National Stage of PCT/EP05/09760, filed Sep. 10,2005, the disclosure of which is incorporated herein by reference in itsentirety. The parent application claims priority to German ApplicationNo. 102004044595.8, filed Sep. 13, 2004, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The production of composite elements composed in particular of metallicouter layers and of a core composed of isocyanate-based foams, mostlypolyurethane (PU) foams or polyisocyanurate (PIR) foams, is nowadayswidely practiced on continuously operating twin-belt systems, and theelements are often also termed sandwich elements. Alongside sandwichelements for cold store insulation, elements with colored outer layersare of constantly increasing importance, these being intended forforming facades on a very wide variety of buildings. The outer layersused here comprise not only coated steel sheet but also stainless steelsheet, copper sheet or aluminum sheet. In particular in the case offacade elements, adhesion between foam and outer layer is decisive. Ifthe color shade is dark, the insulated outward-facing outer layer caneasily reach temperatures around 80° C. If adhesion of the foam to theouter layer is inadequate, blisters are produced on the surface, causedby separation of foam from the sheet, and these make the facadeunattractive. In order to eliminate these problems, adhesion-promoterlacquers are applied before production of the coil is complete. However,reasons related to the process require that additives, such as flowaids, hydrophobicizing agents, de-aerating agents, and the like bepresent in the adhesion-promoter lacquers. These additives sometimesconsiderably impair the polyurethane foaming process. Added to this areinteractions in the steel coil between lacquer on the outward-facingside and on the reverse side. The additional substances thus transferredto the reverse side mostly also have an adverse effect on the PU foamingprocess and lead to defects in the sandwich element. Even the coronatreatment of the outer layers, which is now prior art, is in many casesinadequate to eliminate these defects. Furthermore, a very wide varietyof reasons can prevent ideal adjustment of the twin-belt temperature forthe particular system. This is particularly the case during productionstart-up procedures. This can likewise have an adverse effect on thefoaming process and on the adhesion of the foam to the metallic outerlayers.

Another frequent occurrence in the production of sandwich elements,caused by a wide variety of reasons, is undesired air inclusions, knownas cavities, at the lower and upper outer layer, between sheet metal andrigid polyurethane foam. These air inclusions between sheet metal andfoam can lead to blistering of the sheet metal particularly when severetemperature changes occur in the facade element application. Again, thisthen makes the facade unattractive.

Consequently, there is a requirement to find a process which gives alasting improvement in the adhesion of the PU foams and PIR foams tometallic outer layers and which also withstands adverse externalcircumstances surrounding the production process. The process may beused continuously or batchwise. By way of example, a batchwise mode ofoperation can be used during twin-belt start-up procedures and forcomposite elements produced by means of presses which operate batchwise.Continuous use is required if the PU systems or PIR systems usedintrinsically have very low adhesion to metallic outer layers.

At the same time, formation of cavities should be avoided in thisprocess, in particular at the lower outer layer.

One possible way of improving adhesion is to apply an adhesion promoterto the outer layers. In the case of sandwich elements it is often thelower outer layer which has the poorest adhesion, determined in thetensile test. Furthermore, in conventional structures produced by meansof sandwich elements the sheet-metal lower side is the outward-facingside of the facade and is therefore exposed to extreme conditions, suchas temperature and suction effects, and is therefore subject to greaterstress than the upper side of the sandwich element. For these reasons,it is possible to apply the adhesion promoter only to the lower outerlayer. Once the adhesion promoter has been applied to the lower outerlayer, the PU system or PIR system is applied to the outer layer, thusgiving a composite element whose structure is: outer layer-adhesionpromoter-rigid PU/PIR foam-outer layer.

There is a wide variety of established processes for the application oflacquers, adhesion promoters, adhesives, and thin films generally tosheet metal or to other substrates. Lacquers can be applied tosubstrates by means of dipping, spraying, electrostatic deposition,plasma coating, flow coating, or rolling. It is also possible to usespin coating to produce thin films on a substrate. Here, the substanceis applied to the substrate and the substrate is then rotated, thusdistributing the substance uniformly over the substrate. However,processes of this type are not practical in the case of the sheet metalused for production of sandwich elements.

A process very similar to spin coating likewise utilizes a rotatingapparatus, but here the substance is ejected centrifugally and laterallyvia the rotation of the rotating plate. This technique is particularlygood for internal coating of pipes or of other cavities, as described byway of example in U.S. Pat. No. 3,349,568, DE 2808903 and WO 9959730.One embodiment of this technique serves for the coating of moldings andalso of sheet metal. However, in all of these processes the outer layersto be coated are conducted around the rotating plate and the substanceis always applied to the relevant outer layer by centrifugal ejectionfrom the rotating plate in a lateral direction, as described by way ofexample in DE 2412686. An electrical field is also sometimes appliedhere to improve application. However, all of these processes can formlarge amounts of aerosols which are hazardous to the environment and tohealth.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a rotation plate according to one embodiment of theinvention.

FIG. 2 shows the arrangement of the apparatus according to oneembodiment of the invention.

FIG. 3 shows an arrangement of the equipment according one embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

It was then an object of the present invention to find a suitableprocess for applying an adhesion promoter to horizontal sheet metal orto another outer layer which is continuously transported in a horizontaldirection, since sandwich elements are generally produced using acontinuously operating twin belt. There should be no formation orrelease of aerosols here. Furthermore, the process for applying theadhesion promoter should be substantially maintenance-free.

Surprisingly, the object could be achieved by applying the adhesionpromoter to the outer layer by way of a rotating plate locatedhorizontally, preferably parallel to the outer layer.

The invention therefore provides a process for production of compositeelements composed of at least one outer layer a) and of an rigidisocyanate-based foam b), where between the outer layer a) and the rigidisocyanate-based foam b) an adhesion promoter c) has been applied, andwhere the outer layer a) is continuously moved and the adhesion promoterc) and the starting material for the rigid isocyanate-based foam b) areapplied successively to the outer layer, which comprises applying theadhesion promoter c) by means of a rotating plate which has beeninstalled horizontally or with a deviation of up to 15° from horizontal,preferably parallel to the outer layer.

The invention further provides an apparatus for application of liquidsto a continuously conveyed outer layer, wherein the liquid is applied toa rotating plate which has been installed horizontally and preferablyparallel to and above the outer layer, is ejected centrifugally from therotating plate via rotation and then, via gravity, passes onto the outerlayer.

When the inventive apparatus is used for production of compositeelements comprising isocyanate-based foams, the liquid is preferably anadhesion promoter c).

The adhesion promoter c) used preferably comprises a reactive single- ormulticomponent polyurethane system.

An advantageous process has proven to be one wherein at the juncture ofapplication of the starting material for the rigid isocyanate-based foamb) to the lower outer layer, the adhesion promoter c) has not yetexceeded its open time, i.e. at that juncture the polyurethane systemhas not fully completed its reaction. Control in this respect can beexerted via the distance between the application device for the adhesionpromoter and the apparatus for application of the starting material forthe rigid isocyanate-based foam b), or preferably via adjustment of thereactivity of the adhesion promoter.

Outer layers which may be used comprise gypsum plasterboard, glassnonwovens, aluminum foils, aluminum sheets, copper sheets, or steelsheets, preferably aluminum foils, aluminum sheets, or steel sheets,particularly preferably steel sheets. Coated or uncoated steel sheetsmay be used. They are preferably not corona-treated.

The outer layer is preferably transported with a constant velocity offrom 2 to 15 m/min, preferably from 3 to 12 m/min, particularlypreferably from 3 to 9 m/min. The outer layer here is preferablyhorizontal at least from the application of the polyurethane system b),preferably during the entire period from application of the adhesionpromoter. The adhesion promoter may also be applied when the outer layerhas slight inclination in the direction of transport and is thereforenot conducted horizontally.

In conventional sandwich elements, the rigid isocyanate-based foam isenclosed by an upper and a lower outer layer. It is sufficient for thelower outer layer to be provided with an adhesion promoter.

In the inventive process here, when sheet metal and foils are used asouter layers, the outer layers are successively unwound from a roll,profiled, heated, if appropriate corona-treated in order to increasecoatability by polyurethane, coated with the starting material for therigid isocyanate-based foam b), also often termed PU system or PIRsystem, cured in the twin belt, and finally cut to the desired length.

In principle, the application of the adhesion promoter c) may take placeat any point in the process between unwinding of the outer layers andapplication of the PU system or PIR system.

It is advantageous here for the distance between application of theadhesion promoter c) and application of the PU system or PIR system b)to be small. This minimizes the waste produced at the start and end ofthis process, and also in the event of unforeseen interactions of theproduction process.

The adhesion promoter is discharged by way of a rotating plate which hasbeen installed horizontally, preferably parallel to and above the lowerouter layer, and which can be rotated by way of a drive. The rotatingplate can also be attached with a deviation of up to 15° fromhorizontal. The rotating plate may be round or elliptical. Thelength:width ratio for the rotating plate is preferably from 1 to 1.8,particularly preferably from 1 to 1.4, and in particular from 1.0 to1.25.

The rotating plate may be completely flat, or the edge of the rotatingplate may have been angled-off or rounded-off upward. It is preferablethat the edge of the rotating plate used has been angled-off orrounded-off upward. Holes are introduced into the angled-off section inorder to ensure discharge of the adhesion promoter c). The diameter andnumber of the holes are mutually matched in such a way as to permitmaximum uniformity of application of finely dispersed adhesion promoterc) to the outer layer thereunder, and to permit all of the materialapplied to the rotating plate to be discharged, and to minimize themaintenance cost of the rotating plate. The outer angled-off sectionpreferably has from 4 to 64 holes with a diameter of from 0.5 to 3 mm,preferably from 12 to 40 holes with a diameter of from 1 to 3 mm,particularly preferably from 15 to 30 holes with a diameter of from 1.5to 2.5 mm.

In one embodiment, the design of the rotating plate can be cascade-like.FIG. 1 shows the side view of this type of rotating plate. The cascadeshere have been arranged so as to rise from the axis of rotation (A)outward. At the transitions from one cascade to the adjacent cascade (B)there may be holes introduced into the rotating plate, so that a portionof the adhesion promoter can be discharged onto the lower outer layer atthese cascade transitions. This type of rotating plate designed in themanner of a cascade provides particularly uniform application of theadhesion promoter to the outer layer located therebelow. The applicationof the adhesion promoter to the rotating plate takes place with maximumcloseness to the axis of rotation. Surprisingly, it has been found herethat the adhesion promoter is distributed particularly uniformly ontothe lower outer layer if the point of application of the adhesionpromoter parallel to the direction of production is exactly prior to orsubsequent to the axis of rotation.

The diameter of the rotating plate depends on the width of the outerlayer and is from 0.05 to 0.3 m, preferably from 0.1 to 0.25 m,particularly preferably from 0.12 to 0.22 m, based on the long side. Therotating plate has been installed at a height of from 0.02 to 0.2 m,preferably from 0.03 to 0.18 m, particularly preferably from 0.03 to0.15 m, above the outer layer to be wetted.

A rotating plate having from 2 to 4, preferably from 2 to 3,particularly preferably 2, cascades can be used.

The angle of inclination of the holes which are introduced into therotating plate for the discharge of the adhesion promoter is from about10 to 70°, preferably from 30 to 60°, with respect to the lower outerlayer. The holes may have been introduced at the cascade transitions orelse at the outer angled-off section. The number of holes here increasesfrom cascade to cascade from the inside toward the outside. From 10 to30, preferably from 12 to 25, particularly preferably from 12 to 20,holes whose diameter is from 1.5 to 2.5 mm have been introduced here atthe cascade transition (B) innermost with respect to the axis ofrotation. The number of holes at the outermost angled-off section (C) isfrom 12 to 40, preferably from 12 to 30, particularly preferably from 15to 30, their diameter being from 1.5 to 2.5 mm. In one particularlypreferred embodiment of the rotating plate, the holes at the outerangled-off section are designed so as to alternate with differentinclinations with respect to the outer layer. The ratio of the diametersof adjacent cascades d_(n)/d_(n-1) is from 1.2 to 3, preferably from 2to 2.6.

The wetting radius of the adhesion promoter on the lower outer layer ispreferably from 0.25 to 1 m, with preference from 0.35 to 0.75 m.

The rotation rate of the rotating plate is preferably from 200 to 2500rpm, particularly preferably from 200 to 2000 rpm, and in particularfrom 300 to 1500 rpm.

The amount of the adhesion promoter c) applied to the outer layer isfrom 30-300 g/m², preferably from 40-200 g/m², particularly preferablyfrom 50-120 g/m².

Prior to its application to the rotating plate, the adhesion promoter c)is mixed in a machine, using high- or low-pressure mixers, preferablylow-pressure mixers, and applied to the rotating plate by way of asuitable discharge apparatus, such as a downstream mixing unit. If therotating plate is then rotated by means of a drive, the adhesionpromoter c) is distributed over the surface of the outer layercontinuously conveyed below the rotating plate. By way of example, amixing unit composed of plastic may be used for the mixing andapplication of the adhesion promoter to the rotating plate. The amountof the adhesion promoter c) discharged is matched to the velocity of thecontinuously operating twin belt in such a way as to permit the desiredamount to be applied per m² of sheet metal.

The height of the rotating plate above the lower outer layer, thediameter of the rotating plate, and the speed of rotation, have beenmutually matched in such a way that the adhesion promoter c) dischargedgives maximum uniformity of wetting, extending to the edges, of thesheet metal continuously transported thereunder.

In contrast to the prior art, although the adhesion promoter c) isejected centrifugally and laterally, the result of the low speed ofrotation and the effect of gravity is that it is distributed onto theouter layer located horizontally, preferably parallel to and below therotating plate. Surprisingly, it has now been found that application bymeans of the technique described above forms no aerosol.

The term aerosols is used here for colloidal systems composed of gases,such as air, comprising finely distributed small liquid particles ofdiameter from about 10⁻⁷ to 10⁻³ cm.

Using the small application quantities required for cost-effectiveness,it is not possible to achieve complete wetting of the lower outer layerwith the adhesion promoter c). Surprisingly, however, it has now beenfound that the coating achieved on the lower outer layer by means of theinventive application technique using small application quantities issufficient to achieve a marked improvement in the tensile strengthbetween the treated outer layer and the foam located thereupon, whencomparison is made with untreated sheet metal.

The inventive process can also markedly reduce the proportion ofcavities on the lower outer layer.

Once the adhesion promoter c) has been applied to the lower outer layer,the starting material for the rigid isocyanate-based foam b) is applied.The reactivity of the adhesion promoter c) here is adjusted in such away that the systems b) and c) react with one another (i.e. the opentime of the adhesion promoter c) has not been exceeded at the junctureof application of b)), and cure after a defined time.

Use of the adhesion promoter c) permits lowering of the twin belttemperature, which must normally reach 60° C. for the processing of PIRsystems, to 55° C.

FIG. 2 shows a side view of the inventive apparatus. The adhesionpromoter is applied by way of the metering equipment (2) to the rotatingplate (3) which has been attached horizontally or preferably parallel tothe outer layer (5) and which is rotated by way of the drive (1). It isejected centrifugally (4) from the rotating plate (3) via rotation andpasses by means of gravity onto the outer layer (5).

FIG. 3 shows a plan view of an apparatus for production of sandwichelements, using the inventive apparatus. The following are applied tothe lower outer layer (1): the adhesion promoter c) by way of therotating plate (2), and then the starting material for the rigidisocyanate-based foams b), by way of the foaming portal (3).

Adhesion promoters which may be used are the polyurethane-based adhesionpromoters known from the prior art. These are generally obtainable viareaction of polyisocyanates with compounds having two hydrogen atomsreactive toward isocyanates, the reaction ratio preferably beingselected in such a way that the ratio of the number of isocyanate groupsto the number of groups reactive toward isocyanates in the reactionmixture is from 0.8 to 1.8:1, preferably from 1 to 1.6:1.

Polyisocyanates which may be used are the conventional aliphatic,cycloaliphatic, and in particular aromatic di- and/or polyisocyanates.Preference is given to use of tolylene diisocyanate (TDI),diphenylmethane diisocyanate (MDI), and in particular mixtures composedof diphenylmethane diisocyanate and polyphenylene polymethylenepolyisocyanates (crude MDI).

The isocyanates Lupranat® M 50, Lupranat® M 70 and Lupranat® M 200 fromBASF AG are preferably used here. In one preferred embodiment, theisocyanates used to produce the rigid isocyanate-based foam b) and thoseused to produce the adhesion promoter c) are identical. In one preferredembodiment Lupranat® M 70 is used, and in one particularly preferredembodiment Lupranat® M 200 is used.

Compounds which may be used and have at least two hydrogen atomsreactive toward isocyanate are generally those which have two or morereactive groups in the molecule, selected from OH groups, SH groups, NHgroups, NH₂ groups, and acidic CH groups, e.g. β-diketo groups.

Preference is given to use of polyetherols and/or polyesterols,polyether polyols being particularly preferred. The hydroxyl number ofthe polyetherols and/or polyesterols used is preferably from 25 to 800mg KOH/g, and the molar weights are generally above 400. Thepolyurethanes may be prepared without or with chain extenders and/orcrosslinking agents. Particular chain extenders and/or crosslinkingagents which may be used are di- or trifunctional amines and alcohols,in particular diols and/or triols with molecular weights below 400,preferably from 60 to 300.

The viscosity of the polyol component of the adhesion promoter c) hereis preferably from 100 to 1000 mPas, with preference from 100 to 800mPas, particularly preferably from 150 to 400 mPas (25° C.).

The adhesion promoter may, if appropriate, comprise additives orreactive flame retardants. The amount of these flame retardantsgenerally used is from 0.1 to 30% by weight, based on the total weightof the polyol component.

The reaction of the polyisocyanates with the polyols is preferablycarried out without addition of any physical blowing agents. However,the polyols used may comprise residual water, which acts as a blowingagent. This gives the resultant polyurethane adhesion promoters adensity of from 200 to 1200 g/l, preferably from 400 to 1000 g/l,particularly preferably from 450 to 900 g/l.

The rigid isocyanate-based foams b) used for the inventive process areproduced in a conventional and known manner via reaction ofpolyisocyanates with compounds having at least two hydrogen atomsreactive toward isocyanate groups, in the presence of blowing agents,catalysts, and conventional auxiliaries and/or additives. The followingdetails relate to the starting materials used.

Organic polyisocyanates used are preferably aromatic polyfunctionalisocyanates.

Individual examples which may be mentioned are tolyene 2,4- and2,6-diisocyanate (TDI) and the corresponding isomer mixtures,diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanate (MDI) and thecorresponding isomer mixtures, mixtures composed of diphenylmethane4,4′- and 2,4′-diisocyanates, polyphenyl polymethylene polyisocyanates,mixtures composed of diphenylmethane 4,4′-, 2,4′- and 2,2′-diisocyanatesand of polyphenyl polymethylene polyisocyanates (crude MDI) and mixturescomposed of crude MDI and of tolylene diisocyanates. The organic di- andpolyisocyanates may be used individually or in the form of mixtures.

Use is also often made of what are known as modified polyfunctionalisocyanates, i.e. products obtained via chemical reaction of organic di-and/or polyisocyanates. By way of example, mentioned may be made of di-and/or polyisocyanates containing isocyanurate groups and/or containingurethane groups. The modified polyisocyanates may, if appropriate, bemixed with one another or with unmodified organic polyisocyanates, suchas diphenylmethane 2,4′- or 4,4′-diisocyanate, crude MDI, or tolylene2,4- and/or 2,6-diisocyanate.

Use may also be made here of reaction products of polyfunctionalisocyanates with polyhydric polyols, or else of mixtures of these withother di- and polyisocyanates.

An organic polyisocyanate which has proven particularly successful iscrude MDI with an NCO content of from 29 to 33% by weight and aviscosity at 25° C. in the range from 150 to 1000 meas.

Compounds b) which may be used and have at least two hydrogen atomsreactive toward isocyanate groups are in particular polyether alcoholsand/or polyester alcohols with OH numbers in the range from 25 to 800 mgKOH/g.

The polyester alcohols used are mostly prepared via condensation ofpolyhydric alcohols, preferably diols, having from 2 to 12 carbon atoms,preferably from 2 to 6 carbon atoms, with polybasic carboxylic acidshaving from 2 to 12 carbon atoms, e.g. succinic acid, glutaric acid,adipic acid, suberic acid, azelaic acid, sebacic acid,decanedicarboxylic acid, maleic acid, fumaric acid, or preferablyphthalic acid, isophthalic acid, terephthalic acid, or the isomericnaphthalenedicarboxylic acids.

The polyesterols used mostly have a functionality of from 1.5 to 4.

Polyether polyols particularly used are those prepared by knownprocesses, e.g. via anionic polymerization of alkylene oxides ontoH-functional starter substances in the presence of catalysts, preferablyalkali metal hydroxides.

Alkylene oxides mostly used are ethylene oxide and/or propylene oxide,preferably pure propylene 1,2-oxide.

Starter substances particularly used are compounds having at least 3,preferably from 4 to 8, hydroxy groups or having at least two primaryamino groups in the molecule.

Starter substances used and having at least 3, preferably from 4 to 8,hydroxy groups in the molecule are preferably trimethylolpropane,glycerol, pentaerythritol, sugar compounds, such as glucose, sorbitol,mannitol, and sucrose, polyhydric phenols, resols, e.g. oligomericcondensates composed of phenol and formaldehyde, and Mannich condensatescomposed of phenols, of formaldehyde, and of dialkanolamines, and alsomelamine.

Starter substances used and having at least two primary amino groups inthe molecule are preferably aromatic di- and/or polyamines, such asphenylenediamines, 2,3-, 2,4-, 3,4-, and 2,6-tolylenediamine, and 4,4′-,2,4′-, and 2,2′-diaminodiphenylmethane, and also aliphatic di- andpolyamines, such as ethylenediamine.

The preferred functionality of the polyether polyols is from 3 to 8 andtheir preferred hydroxy numbers are from 25 to 800 mg KOH/g, inparticular from 240 to 570 mg KOH/g.

Other compounds having at least two hydrogen atoms reactive towardisocyanate are crosslinking agents and chain extenders which are usedconcomitantly, if appropriate. Addition of difunctional chain extenders,trifunctional or higher-functionality crosslinking agents, or else, ifappropriate, mixtures of these can prove advantageous for modificationof mechanical properties. Chain extenders and/or crosslinking agentspreferably used are alkanolamines and in particular diols and/or triolswith molecular weights below 400, preferably from 60 to 300.

The amount advantageously used of chain extenders, crosslinking agents,or mixtures of these is from 1 to 20% by weight, preferably from 2 to 5%by weight, based on the polyol component.

The rigid foams are usually produced in the presence of blowing agents,catalysts, flame retardants, and cell stabilizers, and, if necessary, ofother auxiliaries and/or additives.

Water may be used as blowing agent, and reacts with isocyanate groupswith elimination of carbon dioxide. What are known as physical blowingagents may also be used in combination with, or preferably instead of,water. These are compounds inert with respect to the startingcomponents, mostly liquid at room temperature, and evaporating under theconditions of the urethane reaction. The boiling point of thesecompounds is preferably below 50° C. Among the physical blowing agentsare also compounds which are gaseous at room temperature and which areintroduced or dissolved into the starting components under pressure,examples being carbon dioxide, low-boiling alkanes, and fluoroalkanes.

The compounds are mostly selected from the group comprising alkanesand/or cycloalkanes having at least 4 carbon atoms, dialkyl ethers,esters, ketones, acetals, fluoroalkanes having from 1 to 8 carbon atoms,and tetraalkylsilanes having from 1 to 3 carbon atoms in the alkylchain, in particular tetramethylsilane.

Examples which may be mentioned are propane, n-butane, isobutane,cyclobutane, n-pentane, isopentane, cyclopentane, cyclohexane, dimethylether, methyl ethyl ether, methyl butyl ether, methyl formate, acetone,and also fluoroalkanes which can be degraded in the troposphere andtherefore do not damage the ozone layer, e.g. trifluoromethane,difluoromethane, 1,1,1,3,3-pentafluorobutane,1,1,1,3,3-pentafluoropropane, 1,1,1,2-tetrafluoroethane, difluoroethane,and heptafluoropropane. The physical blowing agents mentioned may beused alone or in any desired combinations with one another.

The polyurethane foams or polyisocyanurate foams usually comprise flameretardants. It is preferable to use bromine-free flame retardants. It isparticularly preferable to use flame retardants comprising phosphorusatoms, in particular trischloroisopropyl phosphate, diethylethanephosphonate, triethyl phosphate and/or diphenyl cresyl phosphate.

Catalysts particularly used are compounds which markedly accelerate thereaction of the isocyanate groups with the groups reactive towardisocyanate groups. Catalysts of this type are strongly basic amines,e.g. secondary aliphatic amines, imidazoles, amidines, and alsoalkanolamines, and/or organometallic compounds, in particular thosebased on tin.

If isocyanurate groups are to be incorporated in the rigid foam,specific catalysts are needed. Isocyanurate catalysts usually used aremetal carboxylates, in particular potassium acetate and its solutions.The catalysts may be used alone or in any desired mixtures with oneanother, as required.

Auxiliaries and/or additives which may be used for this purpose aresubstances known per se, e.g. surfactants, foam stabilizers, cellregulators, fillers, pigments, dyes, hydrolysis stabilizers, antistaticagents, fungistatic agents, and bacteriostatic agents.

Further details concerning the conduct of the inventive process,starting materials used, blowing agents, catalysts, and also auxiliariesand/or additives are found by way of example in Kunststoffhandbuch[Plastics Handbook], volume 7, “Polyurethane” [“Polyurethanes”]Carl-Hanser-Verlag Munich, 1st edition, 1966, 2nd edition, 1983, and 3rdedition, 1993.

To produce the rigid isocyanate-based foams, the polyisocyanates and thecompounds having at least two hydrogen atoms reactive toward isocyanategroups are reacted in amounts such that the isocyanate index is in therange from 100 to 220, preferably from 115 to 180, in the case of thepolyurethane foams. The rigid polyurethane foams may be producedbatchwise or continuously with the aid of known mixing apparatus.

It is also possible to operate with an index >180, preferably from 200to 500, particularly preferably from 250 to 500, for production ofpolyisocyanurate foams.

The starting components may be mixed with the aid of known mixingapparatus.

The inventive rigid PU foams are usually produced by the two-componentprocess. In this process, the compounds having at least two hydrogenatoms reactive toward isocyanate groups are mixed with the blowingagents, with the catalysts, and also with the other auxiliaries and/oradditives to give what is known as a polyol component, and this isreacted with the polyisocyanates or mixtures composed of thepolyisocyanates and, if appropriate, blowing agents, also termed theisocyanate component.

The starting components are usually mixed at a temperature of from 15 to35° C., preferably from 20 to 30° C. The reaction mixture may be mixedusing high- or low-pressure feed machines.

The density of the rigid foams used for this purpose is preferably from10 to 400 kg/m³, preferably from 20 to 200 kg/m³, in particular from 30to 100 kg/m³.

The thickness of the composite elements is usually in the range from 5to 250 mm.

EXAMPLES A) Composition of Adhesion Promoter System

A Component

-   -   62 parts of polyetherol 1 composed of propylene glycol and        propylene oxide, functionality 2, hydroxy number 250 mg KOH/g    -   25 parts of polyesterol 1 composed of phthalic anhydride,        diethylene glycol, and oleic acid, functionality 1.8, hydroxy        number 200 mg KOH/g    -   10 parts of trischloroisopropyl phosphate flame retardant, TCPP    -   2 parts of silicone-containing stabilizer    -   1 part of amine-containing PU catalyst

B Component

Isocyanate Lupranat M50, polymeric MDI (BASF AG)

A component and B component were mixed with one another in ratios suchthat the index was in the region of 115. No additional blowing agent wasadded. However, the polyols used comprised residual water, and theresultant density of the cured adhesion promoter was in the region ofabout 560 g/L.

B) Composition of PU System II

A Component

-   -   55.5 parts of polyetherol 1 composed of sorbitol and propylene        oxide, functionality 5, hydroxy number 500 mg KOH/g    -   20 parts of flame retardant 1: trischloroisopropyl phosphate,        TCPP    -   20 parts of flame retardant 2: PHT-4-diol (Great Lakes)    -   1.5 parts of silicone-containing stabilizer    -   3 parts of catalyst 1: amine-containing PU catalyst    -   Blowing agent 1 n-pentane    -   Blowing agent 2 water

B component

Isocyanate Lupranat M50, polymeric MDI (BASF AG)

A component, B component, and blowing agent were reacted in ratios suchthat the index was in the region of 130 and the envelope densityachieved was 43 g/L.

C) Composition of PIR System

A component

-   -   56 parts of polyesterol 1 composed of phthalic anhydride,        diethylene glycol and oleic acid, functionality 1.8, hydroxy        number 200 mg KOH/g    -   10 parts of polyetherol 1 composed of ethylene glycol and        ethylene oxide, functionality 2, hydroxy number 200 mg KOH/g    -   30 parts of flame retardant 1: trischloroisopropyl phosphate,        TCPP    -   1.5 parts of stabilizer 1: silicone-containing stabilizer    -   1.5 parts of catalyst 1: PIR catalyst, salt of a carboxylic acid    -   1 part of catalyst 2: amine-containing PU catalyst    -   Blowing agent 1: n-pentane    -   Blowing agent 2: water

B component

Isocyanate Lupranat M50, polymeric MDI (BASF AG)

A component, B component, and blowing agent were mixed with one anotherin ratios such that the index was in the region of 350 and the envelopedensity achieved was 43 g/L.

The adhesion promoter system was mixed at slightly elevated temperature,from 30 to 50° C., by means of a low-pressure mixing machine (Unipre),and applied to the rotating plate by means of a mixing unit composed ofplastic. The rotating plate had a diameter of 15 cm and had anangled-off edge. The height of the angled-off section was 15 mm. 32holes had been installed near the edge, and the adhesion promoter systemwas ejected through these centrifugally by means of centrifugal force.The speed of rotation was 900 rpm. The width of the twin belt was 1.2 mand it was advanced at a constant velocity of 3 m/min. The amounts ofadhesion promoter discharged were varied in such a way as to giveapplied amounts of 60, 80 and 100 g/m². The temperature of the twin beltwas varied in the range from 55 to 60° C.

The adhesion promoter system c) was applied about 2 m upstream of thefoaming portal. The polyisocyanurate system b) was applied by means ofan oscillating applicator bar with multiple nozzles. The metallic outerlayer was not corona-treated. Once the system had cured, test specimensof dimensions 100×100×5 mm were sawn, and the adhesion of the foam tothe outer layer was determined to DIN EN ISO 527-1/DIN 53292.

The number of cavities was determined visually.

TABLE 1 Experimental parameters and results. Examples 5 and 6 arecomparative examples for production of sandwich elements without use ofadhesion promoter. Amount Exp. applied Temperature of Adhesion AerosolPattern of Number of No. of system I twin belt [N/mm²] formationapplication cavities 1 60 g/m² 60° C. 0.6 no very very small uniform 280 g/m² 60° C. 0.7 no very very small uniform 3 100 g/m²  60° C. 0.8 nouniform very small 4 100 g/m²  55° C. 0.5 no uniform very small 5 — 55°C. 0.12 — — moderate 6 — 60° C. 0.15 — — moderate

The embodiment of the rotating plate was varied in order to achievemaximum uniformity of distribution of the adhesion promoter on the lowerrotation layer.

TABLE 2 Rotating plate geometries used and application patterns observedfor adhesion promoter system c) on the outer layer to be coated.Assessment is made here of the uniformity of application over thesurface of the outer layer. When application is non-uniform, system c)mostly accumulates in the edge zones of the outer layer. Rotating plateAngled- Number of Diameter Speed of Application no. Geometry off holes[mm] rotation [rpm] pattern 1 round no — 150 900 uniform 2 round yes 32150 900 uniform 3 round yes 10 160 700 non-uniform 4 cascade-like yesinner 16; 65, 150 1200 very uniform (2 cascades) outer 20 5 cascade-likeyes inner 12; 75, 260 800 very uniform (2 cascades) outer 24

1. An apparatus for application of liquids to a continuously conveyedouter layer, comprising: a continuously moving outer layer; and arotating plate above the continuously moving outer layer; wherein therotating plate is horizontal and parallel to the outer layer or with adeviation of up to 15° from horizontal, and a liquid applied to therotating plate is ejected centrifugally from the rotating plate viarotation and then, via gravity, passes onto the outer layer below therotating plate.
 2. The apparatus for application of liquids to acontinuously conveyed outer layer according to claim 1, wherein therotating plate is horizontal and parallel to the outer layer.
 3. Theapparatus for application of liquids to a continuously conveyed outerlayer according to claim 1, wherein the rotating plate comprises an edgeregion which is angled-off or rounded-off upward.
 4. The apparatus forapplication of liquids to a continuously conveyed outer layer accordingto claim 3, wherein the edge region comprises holes.
 5. The apparatusfor application of liquids to a continuously conveyed outer layeraccording to claim 4, wherein the edge region comprises from 4 to 64holes.
 6. The apparatus for application of liquids to a continuouslyconveyed outer layer according to claim 5, wherein a diameter of theholes in the edge region is from 1 to 3 mm.
 7. The apparatus forapplication of liquids to a continuously conveyed outer layer accordingto claim 1, wherein the rotating plate comprises cascades arranged torise from an axis of rotation outward.
 8. The apparatus for applicationof liquids to a continuously conveyed outer layer according to claim 7,wherein a transition from one cascade to an adjacent cascade comprisesat least one hole.
 9. The apparatus for application of liquids to acontinuously conveyed outer layer according to claim 2, wherein therotating plate comprises an edge region which is angled-off orrounded-off upward.
 10. The apparatus for application of liquids to acontinuously conveyed outer layer according to claim 9, wherein the edgeregion comprises holes.
 11. The apparatus for application of liquids toa continuously conveyed outer layer according to claim 10, wherein theedge region comprises from 4 to 64 holes.
 12. The apparatus forapplication of liquids to a continuously conveyed outer layer accordingto claim 11, wherein a diameter of the holes in the edge region is from1 to 3 mm.
 13. The apparatus for application of liquids to acontinuously conveyed outer layer according to claim 2, wherein therotating plate comprises cascades arranged to rise from an axis ofrotation outward.
 14. The apparatus for application of liquids to acontinuously conveyed outer layer according to claim 13, wherein atransition from one cascade to an adjacent cascade comprises at leastone hole.